Not very specific. Assume Aviation related. What year? USA?
Since winter of 1917 did not see much action, this answer applies to:
February 1918 proved a bad month for the Royal Naval Air Service flyers.
9th Naval Sqdr lost a triplane on 3 Feb.
8th Naval Sqdr lost a camel 2 days later.
On 18th, 8th Naval Sqdr lost another experienced pilot.
Source: "Who Downed the Aces in WW1" by Norman Franks